Lubricating System for a Two-Stroke Engine

ABSTRACT

A lubricating system for a two-stroke engine is provided in which oil is more reliably pumped into the two-stroke engine. The oil travels through passages that are integrally cast into the cylinder and/or crankcase. The oil may be injected directly into the crankcase chamber or intake passage. The oil pump may be a rotary pump mounted on the crankcase concentric to the crankshaft. It is also possible to not use an oil pump, and have the oil drawn into the engine by vacuum created in the crankcase.

This patent application claims the benefit of and priority of U.S.Provisional Patent Application Ser. No. 61/326,662, entitled“Lubricating. System for a Two Stroke Engine” by Nagesh Mavinahally,David Kostka, and Bernardo Herzer, filed on Apr. 22, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an internal combustion engine. In particularit pertains to a lubricating system for two stroke or two cycle engines.

2. Description of the Related Art

Conventional low cost two stroke engines, particularly the ones used inlawn and garden applications typically mix lubricating oil with the fuelto lubricate the internal parts of the engine. The disadvantage withpre-mixing is that the ratio of fuel to oil is very much dependent onthe manufacturer, duty cycle of the engine, and model of the equipment.Having to use different ratios for different engines/models can confusethe user as to how much oil has to be mixed with the fuel. Secondly, ifthe ratio of fuel to oil is not correct the engine will either be overlylubricated or under lubricated, both of which are detrimental. Aseparate lubrication pump which eliminates the need for pre-mixing theoil with the fuel is known to be used in more expensive two-strokeengines, such as motorcycles and in some lawn and garden equipment, suchas Mitsubishi's 23 cc trimmer engine. The disadvantage with currentsystems are that external fittings and hoses are used to inject oil intothe intake manifold, which can leak oil at the hose or fitting junctionsand add cost to the equipment because of additional parts. Also, inexisting designs, the oil pump is driven by gears and the pump has areciprocating plunger, which adds additional components and cost.

SUMMARY OF THE INVENTION

A new and improved method of lubricating engines is described in thisinvention. In an embodiment, the improved lubricating engine is appliedto a hand-held gaseous fueled two-stroke engines, and lawn and gardenengines in general.

The design described here eliminates the disadvantages of the currentsystems by not having external hoses, fewer parts, and therefore lowersthe cost and increases the robustness of the lubrication system. In oneof the embodiments, the oil passages from the oil tank to the oil pumpand from pump to the engine (into intake passage or crankcase) areintegrally cast into the cylinder and crankcase, thus eliminating theexternal oil pipes/hoses. In another embodiment, the oil pump is arotary pump mounted on the crankcase concentric to the crankshaft. Inyet another embodiment, there is no oil pump, the oil is drawn into theengine by vacuum created in the crankcase during the engine operatingcycle.

The improved two stroke engine is especially well suited for hand held,lawn and garden equipment such as trimmers, blowers, chainsaws,generator engines, and mopeds.

The present invention reduces the number of parts and reduces thepotential for oil leaks between the joints, particularly in the oilsupply line, where the pressure is higher than atmospheric. Theadditional improvement to the oil pump design simplifies theconstruction and operation of the pump by driving the oil pump directlywithout the need for intermediate gears between the drive shaft(crankshaft) and the driven shaft (in the oil pump), or in the lastembodiment, the elimination of the pump entirely.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the advantagesthereof will be readily obtained as the same becomes better understoodby reference to the detailed description when considered in connectionwith the accompanying drawings, wherein:

FIG. 1 shows the front view of an embodiment of the engine with a frontmounted oil pump.

FIG. 2 shows the top sectional view of an embodiment of the engine'scrankcase, crankshaft, and the oil pump.

FIG. 3 shows the sectional side view of an embodiment of the enginehaving direct crankcase oil injection.

FIG. 4 shows the sectional side view of an embodiment of the enginehaving oil injection into intake passage.

FIG. 5 shows the sectional side of an embodiment of the engine having anoil pump concentrically driven off of the crankshaft.

FIG. 6 shows a Gerotor pump as an example of a rotary pump that may beused on an engine.

FIG. 7 shows the sectional side view of an embodiment of an enginehaving no oil pump but rather, a means for crankcase vacuum to draw theoil into the engine.

FIG. 8 shows an embodiment of an engine with an oil reservoir integralwith the plastic housing.

FIG. 9 shows an embodiment of an engine with an oil reservoir integralwith the flywheel housing.

DETAILED DESCRIPTION

FIG. 1 is an embodiment of the present invention. FIG. 1 shows an oilinjected two-stroke engine 200 having an oil tank 220, and an oil pump210 mounted on to the side of the crankcase 242 by screws. The pump 210has a gear 212 and is driven by the crankshaft 208 having a gear 214.The gears 212 and 214 can be of pinion and worm type or any other type.The two-stroke engine 200 can be a liquid or gaseous fueled engine. Theengine 200 has a cylinder 204, crankshaft 208, and intake manifold 218.The rest of the parts necessary for operation of the two-stroke engine,such as piston, connecting rod, muffler, fuel metering device, etc arevery much similar to any two-stroke engine and can be constructed byanyone skilled in the art. The oil supply line 226 from the oilreservoir 220 feeds into the oil pump 210. The oil pump 210 may have anoil return line, not shown here, to return excess oil back into the oilreservoir 220.

FIG. 2 shows the partial top sectional view of the oil injected enginefrom FIG. 1, having an oil pump 210 injecting oil directly into thecrankcase chamber 234. Also shown is the oil pump drive gear 214 whichis located concentrically on the crankshaft 208. The oil supply passage226 from the oil tank to the oil pump, which is cast integrally into thecrankcase 242, is shown.

FIG. 3 shows an embodiment of the sectional side views of the enginefrom FIG. 1, showing the oil passage 224 in the oil pump 210 and the oilpassage 227 in the crankcase 242. The oil passage 224 227 from the pumpto the crankcase chamber 234 has a check valve 231. The check valve 231has a spring 232 and a valve 230. The check valve is a one way valveallowing the oil to flow into the crankcase chamber 234, whilepreventing the crankcase gases from entering the oil pump 210. It alsoprevents the flow of oil into the crankcase when the engine is notoperating. The spring loaded valve shown here is an example of a one wayvalve. It is understood there are many different types of check valves.Another example is a duck bill valve as used in many carburetors or fuelcaps. It is shown in FIGS. 2 and 3 that the length of the oil passagefrom the oil pump 210 to the crankcase chamber 234 is very short and thepassage 227 in the crankcase is directly in line with the outlet passage224 in the pump 210. Also, it is shown that the oil supply line 226 fromthe oil reservoir 220 to the oil pump 210 is through a cast passage 226in the crankcase 242. However, depending on the location of the oilreservoir, a portion of the cast passage 226 can be in the cylinder 204.

FIG. 4 shows another embodiment of the invention where the oil isinjected into the intake passage 230. The construction of the engine 300is similar to the engine of FIG. 3, however, the oil passage 222 fromthe pump to the intake passage 230 terminates at orifice 228 in theintake passage 230. A portion of the cast passage 222 could be in thecrankcase 242 and another portion be in the cylinder 204.

FIG. 5 shows an engine 400 which is another embodiment where the oilpump 330 has a wobble plate or screw 314 concentrically mounted on thecrankshaft 208. The oil pump 330 may have more than one wobble plate orteeth on the screw. Deeply cut grooves in place of wobble plates orscrew teeth on the crankshaft 208 may also be used as a pump. The oilpump 330 has an oil inlet 326, which can be a cast passage. A checkvalve 331 may be integrated into the passage 326 or into the inlet tothe pump 329. The outlet passage 324 from the oil pump 330 may feed theoil directly into the crankcase chamber 234 through passageway 229 andanother check valve 332 at the outlet.

FIG. 6 shows an end view of a gerotor type pump which is yet anotherpump type that may be used in the embodiment depicted in FIG. 5.

All of the embodiments depicted in FIGS. 1 through 6 use pumps of thepositive displacement type, and any type of pump may be used and deemedto be in the spirit and scope of the invention.

FIG. 7 shows another embodiment of an engine. FIG. 7 shows a partialcutaway of a two stroke engine 500 which lubricates the engine withoutthe use of a pump. The system operates by making use of the alternatingpressure and vacuum pulses present in the crankcase chamber 234 causedby the reciprocating action of the piston when the engine is operating.Oil is fed from a reservoir mounted on or integral to the engine throughpassageway 326 until it contacts the crankshaft at orifice 502. Theorifice in the crankcase casting 502 is sized according to the oilrequirements of the engine. Another passage in the crankshaft 501connects to the orifice 502 and passageway 326 at preselected degrees ofcrankshaft rotation so that the flow of oil from the reservoir isconnected to the crankcase chamber 234 when a vacuum is present in thecrankcase chamber 234. At the exit of passageway 501 is a check valveassembly 531 consisting of a check ball 530, a spring 532 and a hollowretaining plug 533. The purpose of the check valve is to close thepassageway when the engine is not operating. When the engine isoperating and the crankshaft 208 is spinning, centrifugal force willcause the ball to retract from the seat in the passageway and flow ofoil into the engine will be unobstructed. It is to be noted that theorientation of the exit of the passageway 501 allows centrifugal forceto aid in the flow of oil during operation of the engine. With thisinvention it is also possible to vary the oil delivery rate to theengine according to it's needs by the size of the orifice 502, thetiming and duration that the orifice 502 is making a connective pathbetween passageways 326 and 501, and by the distance of the exit ofpassageway 501 from the rotational centerline of the crankshaft 208 thusaffecting the amount of centrifugal force acting to aid the flow.

In another embodiment, as shown in FIG. 8, it may be preferable to havethe oil reservoir 220 be an integral part of the plastic housing 410 ofthe small engine. The oil reservoir may also be integral part of thealuminum casting, such as crankcase or flywheel housing 412, as shown inFIG. 9. The oil reservoir may also be in the front on the frontcrankcase.

In FIGS. 8 and 9, it is preferable to have the shape of the reservoir220 as a hemispherical doughnut such that the oil filter 252 is immersedin the oil at all attitudes. Secondly, the oil supply line 250 insidethe oil reservoir 220 is flexible such that it is free to rotate andbend to keep the oil filter 252 in downward position at all attitudes ofthe engine, including but not limited to inverted attitude. That is, theflywheel housing 412 is in upward attitude. The shape of the oilreservoir 220 could also be spherical.

Operation

In a pre-mixed fuel, as in a conventional low cost two-stroke engine,the fuel-oil mixture and air is inducted into the crankcase chamber 234and the oil present in the mixture lubricates the internal parts of theengine, mainly the bearings, the piston and the cylinder. The oilpresent in the mixture, is eventually burned with the fuel in thecombustion chamber. The ratio of fuel to oil is dependent on the enginemanufacturer and ranges anywhere from 20:1 to 50:1, which is quite arange and as such if the user mixes 50:1 oil in an engine that requires20:1 ratio, the engine could easily starve for oil and lead to severedamage. On the other hand excessive oil in the fuel could build upcarbon in the engine, particularly in combustion chamber and exhaustports and lead to poor performance of the engines, and also requirefrequent removal of carbon build up in the engine. Also in enginesequipped with an exhaust catalyst for the purpose of reducing harmfulexhaust emissions, the catalyst can become damaged.

In an embodiment of the present invention, the lubricating oil is storedin an oil reservoir and with the injection of oil directly into thecrankcase chamber, the time taken for purging the system, particularlywhen the oil is refilled into a completely empty reservoir, is veryshort and helps lubricate the engine quickly and prevent any damage thatcould potentially occur to the engine when a longer oil passage is used.

Therefore there are several significant advantages in using the new oilinjected lubricating system in a two-stroke engine. The main advantagesin oil injected two-stroke engines are: 1) The consumer does not have toworry about ratio of oil to fuel. 2) Any type of fuel can be used,including but not limited to LPG fuel. 3) The shape of the oil reservoirlets the user operate the engine in any attitude. 4) Internal castpassages eliminate potential leaks and extra parts. 5) Direct injectionof oil into the crankcase purges the passage faster. 6) Integral oiltank eliminates extra parts (oil reservoir and fasteners). 7) Internalpassages help warm the oil temperature and maintain the optimumviscosity of oil as it enters the crankcase chamber, at very coldambient temperatures.

The present invention has been described in an illustrative manner. Itis to be understood that the terminology which has been used is intendedto be in the nature of words of description rather than of limitation.While there have been described herein, what are considered to bepreferred and exemplary embodiments of the present invention, othermodifications of the invention shall be apparent to those skilled in theart from the teachings herein and, it is, therefore, desired to besecured in the appended claims all such modifications as fall within thetrue spirit and scope of the invention.

1. (canceled)
 2. A lubricating system for a two stroke enginecomprising: an oil pump mounted to the side of the crankcase of said twostroke engine; an oil reservoir and oil supply passage from said oilreservoir to said oil pump, and an oil outlet passage of said oil pumpfor the injection of oil from said oil pump into said crankcase, whereinsaid oil outlet passage is cast integrally into the crankcase.
 3. Thelubricating system of claim 2 further comprising an oil pump drive gearof said oil pump located concentrically on the crankshaft.
 4. Thelubricating system of claim 2 wherein said oil outlet passage of saidoil pump injects oil into a crankcase chamber of said crankcase.
 5. Thelubricating system of claim 4 wherein said oil outlet passage of saidoil pump is directly in line with a crankcase chamber inlet passage ofsaid crankcase chamber.
 6. The lubricating system of claim 4 furthercomprising a check valve for allowing one way flow of oil from said oilpump into said crankcase chamber.
 7. The lubricating system of claim 2wherein said oil outlet passage of said oil pump injects oil into anair/fuel intake port of said crankcase through an internally cast oilpassage.
 8. The lubricating system of claim 2 wherein said oil passagefrom said oil reservoir to said oil pump is cast integrally into saidcrankcase.
 9. The lubricating system of claim 2 wherein said oilreservoir is shaped in a spherical to semi-spherical fashion with an oilsupply line, that has an oil filter at the end, is inside said oilreservoir and said oil supply line is free to rotate, whereby said oilfilter is kept immersed in the oil at all attitudes.
 10. A lubricatingsystem for a two stroke engine comprising: a rotary oil pumpconcentrically mounted on a crankshaft of said engine; an oil reservoir;an oil supply passage from said oil reservoir to said rotary oil pump;and an outlet passage from said oil pump to feed oil directly into acrankcase chamber of said crankcase.
 11. The lubricating system of claim10 further comprising of a check valve integrated into said oil supplypassage.
 12. The lubricating system of claim 10 further comprising of acheck valve integrated into said outlet passage from said oil pump tosaid crankcase chamber.
 13. The lubricating system of claim 10 whereinsaid rotary oil pump is a gerotor type pump.
 14. The lubricating systemof claim 10 wherein said oil reservoir is shaped in a spherical tosemi-spherical fashion with an oil supply line, that has an oil filterat the end, is inside said oil reservoir and said oil supply line isfree to rotate, whereby said oil filter is kept immersed in the oil atall attitudes.
 15. A lubricating system for a two stroke enginecomprising: an oil reservoir; an oil supply passage from said oilreservoir to a crankshaft of said engine, wherein said oil supplypassage is cast integrally into a crankcase of said engine and said oilsupply passage terminates at a oil supply passage ending orifice; and acrankshaft passage within said crankcase, beginning at a crankshaftpassage beginning orifice and terminating into a crankcase chamber ofsaid crankcase, wherein said oil supply passage ending orifice connectsto crankshaft passage beginning orifice at preselected degrees ofcrankshaft rotation such that the flow of oil from said oil reservoirinto said crankcase chamber occurs through the presence of a vacuum insaid crankcase chamber.
 16. The lubricating system of claim 15 furthercomprising of a check valve at the exit of said crankshaft passage toclose said crankshaft passage when said engine is not operating.
 17. Thelubricating system of claim 16 wherein said check valve is comprised ofa checkball, a spring, and a hollow retaining plug, such that when saidengine is operating and said crankshaft is spinning, centrifugal forcecauses the ball to retract from its seat in said crankshaft passage,unobstructing the flow of oil into said engine.
 18. The lubricatingsystem of claim 15 wherein said oil reservoir is shaped in a sphericalto semi-spherical fashion with an oil supply line, that has an oilfilter at the end, is inside said oil reservoir and said oil supply lineis free to rotate, whereby said oil filter is kept immersed in the oilat all attitudes.